This invention relates to high-solids coating compositions and more particularly to high-solids coating compositions exhibiting improved drying and film characteristics.
The use of various polyvalent metal salts, and in particular transition metal salt compositions, as driers or siccatives for paints, varnishes and inks is well known. Such metal salts also have been described as "drier catalysts". Such drier catalysts promote the oxidative polymerization of the unsaturated oils in the coating compositions after application in order to effect drying. Lead, cobalt, manganese, zirconium, rare earth and calcium soaps are among those commonly employed for this purpose. Commercial driers ordinarily are dissolved in any of various solvents suitable for the purpose, most usually in petroleum distillates such as those commonly termed petroleum spirits, mineral spirits, etc.
For many years, curable coating compositions useful as paints, varnishes, etc., were dissolved in volatile hydrocarbon solvents to facilitate the deposition of thin films on the substrates to be coated and to enable the solvent to evaporate into the atmosphere within a reasonable period of time leaving a dry non-tacky coating. The use of such volatile hydrocarbon solvents as diluents, therefore, results in air pollution problems.
More recently, the coatings industry has directed its attention to the problem of volatile organic emissions from organic coating compositions. These efforts have been encouraged by various governmental and state agencies concerned with the air pollution caused by the use of volatile hydrocarbon solvents. Such efforts by the coatings industry have resulted in the development of a number of high-solids resin coating formulations which contain significantly reduced amounts of solvents, and, in some instances, little or no solvent. In those instances, the volatile hydrocarbon solvents have sometimes been replaced by reactive diluents such as monoethylenically unsaturated monomers containing a vinyl group. Such reactive diluents may be, for example, vinyl compounds such as vinyl toluene, vinyl chloride, vinyl esters of alkanoic acids, or acrylic monomers such as acrylic acid, methacrylic acid, or esters of acrylic or methacrylic acid.
U.S. Pat. No. 4,100,133 describes air-dried curable compositions which comprise dicyclopentenyl acrylate or methacrylate and non-volatile reactive monomer, polyvalent metal-containing complexes such as cobalt naphthenate and a volatile oxime stabilizer. Such compositions are characterized by the fact that they can have exceptionally high-solids content and rapid cure by air-drying. High-solids alkyd resin coatings are described in U.S. Pat. No. 4,624,869. The alkyd coatings are modified to include an unsaturated polyester or unsaturated polyester urethane cure modifier. The process also is reported to be useful on acrylic and polyester resins.
U.S. Pat. No. 4,633,001 describes a method of preparing transition metal salt compositions of organic carboxylic acids having improved properties. The patent also describes a variety of uses for the transition metal salts including the use in paint formulations and in curing of unsaturated polyester resin compositions.
Although the reactive diluent developments have provided reduced solvent emission and high-solids coatings, such systems often exhibit a slow dry and film cure on application. Many of the drier catalysts which have been useful as driers for hydrocarbon-diluted organic coating formulations are observed to be inadequate when used in high-solids coating formulations.
It has been observed that such high-solids coating compositions often cannot be cured to acceptable coatings within a reasonable amount of time, and often not at all, when many of the known resin driers are utilized in conventional quantities, which is generally less than about 0.5% by weight in terms of metal relative to the amount of vehicle solids.
In particular, unacceptably long through dry cure times have generally been "solved" by using extremely high amounts of zirconium drier (e.g., amounts greater than 0.7% by weight as metal per unit weight of vehicle solids). These high amounts of zirconium drier are uneconomical at best and often still do not achieve the desired performance characteristics. The inventors have discovered that neodymium salts provide the desired drying characteristics and result in the formation of coating films having the desired properties.